Thermoacoustic device

ABSTRACT

A thermoacoustic device includes a sound wave generator and a signal input device. The sound wave generator includes a graphene layer. The graphene layer includes at least one graphene. The signal input device inputs signals to the sound wave generator.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/335,041, filed on Dec. 22, 2011, entitled“THERMOACOUSTIC DEVICE,” which claims all benefits accruing under 35U.S.C. §119 from China Patent Application No. 201110076702.4, filed onMar. 29, 2011; No 201110076700.5, filed on Mar. 29, 2011; No.201110076749.0, filed on Mar. 29, 2011; No. 201110076754.1, filed onMar. 29, 2011; No. 201110076698.1, filed on Mar. 29, 2011; No.201110076762.6, filed on Mar. 29, 2011; No. 201110076761.1, filed onMar. 29, 2011; and No. 201110076748.6, filed on Mar. 29, 2011, in theChina Intellectual Property Office, the disclosures of which areincorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to acoustic devices and, particularly, toa thermoacoustic device.

2. Description of Related Art

Acoustic devices generally include a signal device and a sound wavegenerator electrically connected to the signal device. The signal deviceinputs signals to the sound wave generator, such as loudspeakers. Aloudspeaker is an electro-acoustic transducer that converts electricalsignals into sound.

There are different types of loudspeakers that can be categorizedaccording to their working principle, such as electro-dynamicloudspeakers, electromagnetic loudspeakers, electrostatic loudspeakers,and piezoelectric loudspeakers. These various types of loudspeakers usemechanical vibration to produce sound waves. In other words they allachieve “electro-mechanical-acoustic” conversion. Among the varioustypes, the electro-dynamic loudspeakers are the most widely used.

A thermophone based on the thermoacoustic effect was made by H. D.Arnold and I. B. Crandall (H. D. Arnold and I. B. Crandall, “Thethermophone as a precision source of sound,” Phys. Rev. 10, pp 22-38(1917)). However, the thermophone adopting the platinum strip producesweak sounds because the heat capacity per unit area of the platinumstrip is too high.

What is needed, therefore, is to provide a thermoacoustic device havinggood sound effect and high efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic top plan view of one embodiment of athermoacoustic device.

FIG. 2 is a cross-sectional view taken along a line II-II of thethermoacoustic device in FIG. 1.

FIG. 3 is a Scanning Electron Microscope (SEM) image of a drawn carbonnanotube film.

FIG. 4 is an SEM image of a flocculated carbon nanotube film.

FIG. 5 is an SEM image of a pressed carbon nanotube film.

FIG. 6 is an SEM image of a carbon film.

FIG. 7 shows a transmittance graph of an embodiment of the carbon film.

FIG. 8 is a schematic top plan view of one embodiment of athermoacoustic device.

FIG. 9 is a cross-sectional view taken along a line IX-IX of thethermoacoustic device in FIG. 8.

FIG. 10 is a schematic top plan view of one embodiment of athermoacoustic device.

FIG. 11 is a cross-sectional view taken along a line XI-XI of thethermoacoustic device in FIG. 10 according to one example.

FIG. 12 is a cross-sectional view taken along a line XI-XI of thethermoacoustic device in FIG. 10 according to another example.

FIG. 13 is a schematic top plan view of one embodiment of athermoacoustic device.

FIG. 14 is a cross-sectional view taken along a line XVI-XVI of thethermoacoustic device in FIG. 13.

FIG. 15 is an SEM image of an untwisted carbon nanotube wire.

FIG. 16 is an SEM image of a twisted carbon nanotube wire.

FIG. 17 is a schematic cross-sectional view of one embodiment of athermoacoustic device including a carbon nanotube composite structureused as a substrate.

FIG. 18 is a schematic top plan view of one embodiment of athermoacoustic device.

FIG. 19 is a cross-sectional view taken along a line XIX-XIX of thethermoacoustic device in FIG. 18.

FIG. 20 is a schematic top plan view of one embodiment of athermoacoustic device.

FIG. 21 is a cross-sectional view taken along a line XXI-XXI of thethermoacoustic device in FIG. 20.

FIG. 22 is a cross-sectional side view of one embodiment of athermoacoustic device.

FIG. 23 is a cross-sectional side view of one embodiment of athermoacoustic device.

FIG. 24 is a cross-sectional side view of one embodiment of athermoacoustic device.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIGS. 1 and 2, a thermoacoustic device 10 in one embodimentincludes a sound wave generator 102 and a signal input device 104. Thesound wave generator 102 is capable of producing sounds by athermoacoustic effect. The signal input device 104 is configured toinput signals to the sound wave generator 102 to generate heat.

Sound Wave Generator

The sound wave generator 102 has a very small heat capacity per unitarea. The sound wave generator 102 can be a conductive structure with asmall heat capacity per unit area and a small thickness. The sound wavegenerator 102 can have a large specific surface area for causing thepressure oscillation in the surrounding medium by the temperature wavesgenerated by the sound wave generator 102. The sound wave generator 102can be a free-standing structure. The term “free-standing” includes, butis not limited to, a structure that does not have to be supported by asubstrate and can sustain the weight of it when it is hoisted by aportion thereof without any significant damage to its structuralintegrity. That is to say, at least part of the sound wave generator canbe suspended. The suspended part of the sound wave generator 102 willhave more sufficient contact with the surrounding medium (e.g., air) tohave heat exchange with the surrounding medium from both sides of thesound wave generator 102. The sound wave generator 102 is athermoacoustic film. The sound wave generator 102 has a small heatcapacity per unit area and a large surface area for causing the pressureoscillation in the surrounding medium by the temperature waves generatedby the sound wave generator 102.

In some embodiments, the sound wave generator 102 can be or include agraphene layer. A thickness of the graphene layer can be less than 10micrometers. In some embodiments, the thickness of the graphene layer isin a range from about 10 nanometers to about 200 nanometers. Thegraphene layer includes at least one graphene. The graphene is aone-atom-thick planar sheet of sp²-bonded carbon atoms that are denselypacked in a honeycomb crystal lattice. The size of the graphene can bevery large (e.g., several millimeters). However, the size of thegraphene is generally less than 10 microns (e.g., 1 micron). In oneembodiment, the graphene layer is a pure structure of graphene. Thegraphene layer can be or include a single graphene or a plurality ofgraphenes. In one embodiment, the graphene layer includes a plurality ofgraphenes, the plurality of graphenes is stacked with each other orlocated side by side. The plurality of graphenes is combined with eachother by van der Waals attractive force. The graphene layer can be acontinuous integrated structure. The term “continuous integratedstructure” includes, but is not limited to a structure that is combinedby a plurality of chemical covalent bonds (e.g., sp² bonds, sp¹ bonds,or sp³ bonds) to form an overall structure. A thickness of the graphenelayer can be less than 1 millimeter. A heat capacity per unit area ofthe graphene layer can be less than or equal to about 2×10⁻³ J/cm²*K. Insome embodiments, a heat capacity per unit area of the graphene layerconsisting of one graphene can be less than or equal to about 5.57×10⁻⁷J/cm²*K. The graphene layer can be a free-standing structure. Thegraphene has large specific surface. A transmittance of visible light ofthe graphene layer can be in a range from 67% to 97.7%.

In other embodiments, the sound wave generator 102 can be or includes acarbon film. The carbon film includes at least one carbon nanotube layerand at least one the grapheme layer. In some embodiments, the carbonfilm can consist only of the carbon nanotube layer and the graphenelayer. The at least one carbon nanotube layer and the at least onegraphene are stacked with each other. The carbon film can include anumber of carbon nanotube layers and a number of graphene layersalternatively stacked on each other. The carbon nanotube layer and thegrapheme layer can combine with each other via van der Waals attractiveforce. The carbon nanotube layer can include a plurality of microporesdefined by adjacent carbon nanotubes, and the graphene layer covers theplurality of micropores. Diameters of the micropores can be in a rangefrom about 1 micrometer to about 20 micrometers. A thickness of thecarbon film can be in a range from 10 nanometers to about 1 millimeter.Length and width of the carbon film are not limited.

The carbon nanotube layer includes a number of carbon nanotubes. Thecarbon nanotube layer can be a pure structure of carbon nanotubes. Thecarbon nanotubes in the carbon nanotube layer are combined by van derWaals attractive force therebetween. The carbon nanotube layer has alarge specific surface area (e.g., above 30 m²/g). The larger thespecific surface area of the carbon nanotube layer, the smaller the heatcapacity per unit area will be. The smaller the heat capacity per unitarea, the higher the sound pressure level of the sound produced by thesound wave generator 102. The thickness of the carbon nanotube layer canrange from about 0.5 nanometers to about 1 millimeter. The carbonnanotube layer can include a number of pores. The pores are defined byadjacent carbon nanotubes. A diameter of the pores can be less 50millimeters, in some embodiment, the diameter of the pores is less 10millimeters. A heat capacity per unit area of the graphene layer can beless than or equal to about 2×10⁻³ J/cm²*K. In some embodiment, a heatcapacity per unit area of the graphene layer can be less than or equalto about 5.57×10⁻⁷ J/cm²*K.

The carbon nanotubes in the carbon nanotube layer can be orderly ordisorderly arranged. The term ‘disordered carbon nanotube layer’ refersto a structure where the carbon nanotubes are arranged along differentdirections, and the aligning directions of the carbon nanotubes arerandom. The number of the carbon nanotubes arranged along each differentdirection can be almost the same (e.g. uniformly disordered). The carbonnanotubes in the disordered carbon nanotube layer can be entangled witheach other. The carbon nanotube layer including ordered carbon nanotubesis an ordered carbon nanotube layer. The term ‘ordered carbon nanotubelayer’ refers to a structure where the carbon nanotubes are arranged ina consistently systematic manner, e.g., the carbon nanotubes arearranged approximately along a same direction and/or have two or moresections within each of which the carbon nanotubes are arrangedapproximately along a same direction (different sections can havedifferent directions). The carbon nanotubes in the carbon nanotube layercan be single-walled, double-walled, or multi-walled carbon nanotubes.The carbon nanotube layer can include at least one carbon nanotube film.In other embodiments, the carbon nanotube layer is composed of onecarbon nanotube film or at least two carbon nanotube films. In otherembodiment, the carbon nanotube layer consists of one carbon nanotubefilm or at least two carbon nanotube films.

In one embodiment, the carbon nanotube film can be a drawn carbonnanotube film. Referring to FIG. 3, the drawn carbon nanotube filmincludes a number of successive and oriented carbon nanotubes joinedend-to-end by van der Waals attractive force therebetween. The drawncarbon nanotube film can have a large specific surface area (e.g., above100 m²/g). The drawn carbon nanotube film is a freestanding film. Eachdrawn carbon nanotube film includes a number of successively orientedcarbon nanotube segments joined end-to-end by van der Waals attractiveforce therebetween. Each carbon nanotube segment includes a number ofcarbon nanotubes substantially parallel to each other, and joined by vander Waals attractive force therebetween. Some variations can occur inthe drawn carbon nanotube film. The carbon nanotubes in the drawn carbonnanotube film are oriented along a preferred orientation. The drawncarbon nanotube film can be treated with an organic solvent to increasethe mechanical strength and toughness of the drawn carbon nanotube filmand reduce the coefficient of friction of the drawn carbon nanotubefilm. The thickness of the drawn carbon nanotube film can range fromabout 0.5 nanometers to about 100 micrometers. The drawn carbon nanotubefilm can be used as a carbon nanotube layer directly.

The carbon nanotubes in the drawn carbon nanotube film can besingle-walled, double-walled, or multi-walled carbon nanotubes. Thediameters of the single-walled carbon nanotubes can range from about 0.5nanometers to about 50 nanometers. The diameters of the double-walledcarbon nanotubes can range from about 1 nanometer to about 50nanometers. The diameters of the multi-walled carbon nanotubes can rangefrom about 1.5 nanometers to about 50 nanometers. The lengths of thecarbon nanotubes can range from about 200 micrometers to about 900micrometers.

The carbon nanotube layer can include at least two stacked drawn carbonnanotube films. The carbon nanotubes in the drawn carbon nanotube filmare aligned along one preferred orientation, an angle can exist betweenthe orientations of carbon nanotubes in adjacent drawn carbon nanotubefilms, whether stacked or adjacent. An angle between the aligneddirections of the carbon nanotubes in two adjacent drawn carbon nanotubefilms can range from about 0 degrees to about 90 degrees (e.g. about 15degrees, 45 degrees or 60 degrees).

In other embodiments, the carbon nanotube film can be a flocculatedcarbon nanotube film. Referring to FIG. 4, the flocculated carbonnanotube film can include a plurality of long, curved, disordered carbonnanotubes entangled with each other. The carbon nanotubes can besubstantially uniformly dispersed in the carbon nanotube film. Adjacentcarbon nanotubes are acted upon by van der Waals attractive force toobtain an entangled structure with micropores defined therein. Becausethe carbon nanotubes in the carbon nanotube film are entangled with eachother, the carbon nanotube layer employing the flocculated carbonnanotube film has excellent durability, and can be fashioned intodesired shapes with a low risk to the integrity of the carbon nanotubelayer. The thickness of the flocculated carbon nanotube film can rangefrom about 0.5 nanometers to about 1 millimeter.

Referring to FIG. 5, in other embodiments, the carbon nanotube film canbe a pressed carbon nanotube film. The pressed carbon nanotube film isformed by pressing a carbon nanotube array. The carbon nanotubes in thepressed carbon nanotube film are arranged along a same direction oralong different directions. The carbon nanotubes in the pressed carbonnanotube film can rest upon each other. Adjacent carbon nanotubes areattracted to each other and are joined by van der Waals attractiveforce. An angle between a primary alignment direction of the carbonnanotubes and a surface of the pressed carbon nanotube film is about 0degrees to approximately 15 degrees. The greater the pressure applied,the smaller the angle obtained. In one embodiment, the carbon nanotubesin the pressed carbon nanotube film are arranged along differentdirections, the carbon nanotubes can be uniformly arranged in thepressed carbon nanotube film. Some properties of the pressed carbonnanotube film are the same properties along the direction parallel tothe surface of the pressed carbon nanotube film, such as conductivity,intensity, etc. The thickness of the pressed carbon nanotube film canrange from about 0.5 nanometers to about 1 millimeter.

In one embodiment according to FIG. 6, the sound wave generator 102 is acarbon film consisting of one carbon nanotube layer stacked with onegraphene layer. The carbon nanotube layer consists of two stacked drawncarbon nanotube films. The angle between the alignment directions of thecarbon nanotubes in the two adjacent drawn carbon nanotube films isabout 90 degrees. The graphene layer is a single layer of graphene.Referring to FIG. 7, a transmittance of visible light of the carbon filmis larger than 60%. The thermoacoustic device 10 using the carbon filmas the sound wave generator 102 can be a transparent device.

The graphene layer is very compact, but it has low strength. The carbonnanotube layer has high strength and includes a mount of micropores; andthe carbon film including the carbon nanotube layer and the graphenelayer has an advantage of compactness and high strength. When the carbonfilm is used as the sound wave generator 102, because the graphene layercovers the micropores in the carbon nanotube layer, and the carbon filmhas a larger contacting area with the surrounding medium, the sound wavegenerator has a higher efficiency. The thickness of the carbon nanotubelayer and the graphene layer can be very thin, and a thickness and aheat capacity of the carbon film can be minimal, which makes the soundwave generator have a good sound effect and high sensitivity.

The thermoacoustic device 10 has a wide frequency response range and ahigh sound pressure level. The sound pressure level of the sound wavesgenerated by an embodiment of the thermoacoustic device 10 can begreater than 50 dB. The frequency response range of the thermoacousticdevice 10 can be from about 1 Hz to about 100 KHz with a power input of4.5 W. The total harmonic distortion of the thermoacoustic device 10 isextremely small, e.g., less than 3% in a range from about 500 Hz to 40KHz. The thermoacoustic device 10 can be used in many apparatus, suchas, telephone, Mp3, Mp4, TV, computer. Further, because thethermoacoustic device 10 can be transparent, it can be stuck on a screendirectly.

Energy Generator

The signal input device 104 is used to input signals into the sound wavegenerator. The signals can be electrical signals, optical signals orelectromagnetic wave signals. With variations in the application of thesignals and/or strength applied to the sound wave generator 102, thesound wave generator 102 according to the variations of the signalsand/or signal strength produces repeated heating. Temperature waves,which are propagated into surrounding medium, are obtained. Thesurrounding medium is not limited, just to make sure that a resistanceof the surround medium is larger than a resistance of the sound wavegenerator 102. The surrounding medium can be air, water or organicliquid. The temperature waves produce pressure waves in the surroundingmedium, resulting in sound generation. In this process, it is thethermal expansion and contraction of the medium in the vicinity of thesound wave generator 102 that produces sound. This is distinct from themechanism of the conventional loudspeaker, in which the mechanicalmovement of the diaphragm creates the pressure waves.

In the embodiment according to FIGS. 1 and 2, the signal input device104 includes a first electrode 104 a and a second electrode 104 b. Thefirst electrode 104 a and the second electrode 104 b are electricallyconnected with the sound wave generator 102 and input electrical signalsto the sound wave generator 102. The sound wave generator 102 canproduce joule heat. The first electrode 104 a and the second electrode104 b are made of conductive material. The shape of the first electrode104 a or the second electrode 104 b is not limited and can be lamellar,rod, wire, and block among other shapes. A material of the firstelectrode 104 a or the second electrode 104 b can be metals, conductiveadhesives, carbon nanotubes, and indium tin oxides among otherconductive materials. The first electrode 104 a and the second electrode104 b can be metal wire or conductive material layers, such as metallayers formed by a sputtering method, or conductive paste layers formedby a method of screen-printing.

In some embodiments, the first electrode 104 a and the second electrode104 b can be a linear carbon nanotube structure. The linear carbonnanotube structure includes a plurality of carbon nanotubes joined endto end. The plurality of carbon nanotubes is parallel with each otherand oriented along an axial direction of the linear carbon nanotubestructure. In one embodiment, the linear carbon nanotube structure is apure structure consisting of the plurality of carbon nanotubes.

The first electrode 104 a and the second electrode 104 b can beelectrically connected to two terminals of an electrical signal inputdevice (such as a MP3 player) by a conductive wire. The first electrode104 a and the second electrode 104 b can be parallel with each other. Ifthe carbon nanotube layer includes a plurality of carbon nanotubesoriented in a same direction, the direction can be parallel with thefirst electrode 104 a and the second electrode 104 b. That is to say,the carbon nanotubes are oriented from the first electrode 104 a to thesecond electrode 104 b. Thus, electrical signals output from theelectrical signal device can be input into the sound wave generator 102through the first and second electrodes 104 a, 104 b. In one embodiment,the sound wave generator 102 is a drawn carbon nanotube film drawn fromthe carbon nanotube array, and the carbon nanotubes in the carbonnanotube film are aligned along a direction from the first electrode 104a to the second electrode 104 b. The first electrode 104 a and thesecond electrode 104 b can both have a length greater than or equal tothe carbon nanotube film width.

A conductive adhesive layer can be further provided between the firstand second electrodes 104 a, 104 b and the sound wave generator 102. Theconductive adhesive layer can be applied to a surface of the sound wavegenerator 102. The conductive adhesive layer can be used to providebetter electrical contact and attachment between the first and secondelectrodes 104 a, 104 b and the sound wave generator 102.

The first electrode 104 a and the second electrode 104 b can be used tosupport the sound wave generator 102. In one embodiment, the firstelectrode 104 a and the second electrode 104 b are fixed on a frame, andthe sound wave generator 102 is supported by the first electrode 104 aand the second electrode 104 b.

In one embodiment according to FIGS. 18 and 19, a thermoacoustic device60 can include a plurality of alternatively arranged first and secondelectrodes 104 a, 104 b. The first electrodes 104 a and the secondelectrodes 104 b can be arranged as a staggered manner of +−+−. All thefirst electrodes 104 a are electrically connected together, and all thesecond electrodes 104 b are electrically connected together, whereby thesections of the sound wave generator 102 between the adjacent firstelectrode 104 a and the second electrode 104 b are in parallel. Anelectrical signal is conducted in the sound wave generator 102 from thefirst electrodes 104 a to the second electrodes 104 b. By placing thesections in parallel, the resistance of the thermoacoustic device 60 isdecreased. Therefore, the driving voltage of the thermoacoustic device60 can be decreased with the same effect.

The first electrodes 104 a and the second electrodes 104 b can besubstantially parallel to each other with a same distance between theadjacent first electrode 104 a and the second electrode 104 b. In someembodiments, the distance between the adjacent first electrode 104 a andthe second electrode 104 b can be in a range from about 1 millimeter toabout 3 centimeters.

To connect all the first electrodes 104 a together, and connect all thesecond electrodes 104 b together, a first conducting member 610 and asecond conducting member 612 can be arranged. All the first electrodes104 a are connected to the first conducting member 610. All the secondelectrodes 104 b are connected to the second conducting member 612.

The first conducting member 610 and the second conducting member 612 canbe made of the same material as the first and second electrodes 104 a,104 b, and can be perpendicular to the first and second electrodes 104a, 104 b.

Referring to FIG. 19, the sound wave generator 102 is supported by thefirst electrode 104 a and the second electrode 104 b.

Substrate

Referring to FIGS. 18 and 19, the thermoacoustic device 60 can furtherinclude a substrate 208, the sound wave generator 102 can be disposed onthe substrate 208. The shape, thickness, and size of the substrate 208is not limited. A top surface of the substrate 208 can be planar or havea curve. A material of the substrate 208 is not limited, and can be arigid or a flexible material. The resistance of the substrate 208 isgreater than the resistance of the sound wave generator 102 to avoid ashort circuit through the substrate 208. The substrate 208 can have agood thermal insulating property, thereby preventing the substrate 208from absorbing the heat generated by the sound wave generator 102. Thematerial of the substrate 208 can be selected from suitable materialsincluding, plastics, ceramics, diamond, quartz, glass, resin and wood.In one embodiment according to FIGS. 18 and 19, the substrate 208 is aglass square board with a thickness of about 20 millimeters and a lengthof each side of the substrate 208 of about 17 centimeters. In theembodiment according to FIG. 19, the sound wave generator 102 issuspended above the top surface of the substrate 208 via the pluralityof first electrodes 104 a and the second electrode 104 b. The pluralityof first electrodes 104 a and the second electrodes 104 b are locatedbetween the sound wave generator 102 and the substrate 208. Part of thesound wave generator 102 is hung in air via the first, second electrodes104 a, 104 b. A plurality of interval spaces 601 is defined by thesubstrate 208, the sound wave generator 102 and adjacent electrodes.Thus, the sound wave generator 102 can have greater contact and heatexchange with the surrounding medium.

Because the graphene layer and the carbon nanotube layer both have largespecific surface areas and can be naturally adhesive, the sound wavegenerator 102 can also be adhesive. Therefore, the sound wave generator102 can directly adhere to the top surface of the substrate 208 or thefirst, second electrodes 104 a, 104 b. When the sound wave generator 102is the carbon film including at least one carbon nanotube layer and atleast one graphene layer, the at least one carbon nanotube layer candirectly contact with the surface of the substrate 208 or the first,second electrodes 104 a, 104 b. Alternatively, the at least one graphenelayer can directly contact with the surface of the substrate 208 or thefirst, second electrodes 104 a, 104 b.

In other embodiment, the sound wave generator 102 can be directlylocated on the top surface of the substrate 208, and the first, secondelectrodes 104 a, 104 b are located on the sound wave generator. Thesound wave generator 102 is located between the first, second electrodes104 a, 104 b and the substrate 208. The substrate 208 can further defineat least one recess through the top surface. By provision of the recess,part of the sound wave generator 102 can be hung in the air via therecess. Therefore, the part sound wave generator 102 above the recesscan have greater contact and heat exchange with the surrounding medium.Thus, the electrical-sound transforming efficiency of the thermoacousticdevice 10 can be greater than when the entire sound wave generator 102is in contact with the top surface of the substrate 208. An openingdefined by the recess at the top surface of the substrate 208 can berectangular, polygon, flat circular, I-shaped, or any other shape. Thesubstrate 208 can define a number of recesses through the top surface.The number of recesses can be parallel to each other. According todifferent materials of the substrate 208, the recesses can be formed bymechanical methods or chemical methods, such as cutting, burnishing, oretching. A mold with a predetermined shape can also be used to definethe recesses on the substrate 208.

Referring to FIGS. 8 and 9, in one embodiment of a thermoacoustic device20, each recess 208 a is a round through hole. The diameter of thethrough hole can be about 0.5 μm. A distance between two adjacentrecesses 208 a can be larger than 100 μm. An opening defined by therecess 208 a at the top surface of the substrate 208 can be round. It isto be understood that the opening defined by the recess 208 a can alsohave be rectangular, triangle, polygon, flat circular, I-shaped, or anyother shape.

In one embodiment of a thermoacoustic device 30 according to FIG. 10,each recess 208 a is a groove. The groove can be blind or through. Inthe embodiment according to FIG. 11, the substrate 208 includes aplurality of blind grooves having square strip shaped openings on thetop surface of the substrate 208. In the embodiment according to FIG.12, the substrate 208 includes a plurality of blind grooves havingrectangular strip shaped openings. The blind grooves can be parallel toeach other and located apart from each other for the same distance.

Referring to FIG. 13, in one embodiment of a thermoacoustic device 40,the substrate 208 has a net structure. The net structure includes aplurality of first wires 2082 and a plurality of second wires 2084. Theplurality of first wires 2082 and the plurality of second wires 2084cross with each other to form a net-structured substrate 208. Theplurality of first wires 2082 is oriented along a direction of L1 anddisposed apart from each other. The plurality of second wires 2084 isoriented along a direction of L2 and disposed apart from each other. Anangle α defined between the direction L1 and the direction L2 is in arange from about 0 degrees to about 90 degrees. In one embodiment,according to FIG. 13, the direction L1 is substantially perpendicularwith the direction L2, e.g. α is about 90 degrees. The first wires 2082can be located on the same side of the second wires 2084. In theintersections between the first wires 2082 and the second wires 2084,the first wires 2082 and the second wires 2084 are fixed by adhesive orjointing method. If the either one of the first wires 2082 or the secondwires 2084 have a low melting point, the first wires 2082 and the secondwires 2084 can join with each other by a heat-pressing method. In oneembodiment according to FIG. 14, the plurality of first wires 2082 andthe plurality of second wires 2084 are weaved together to form thesubstrate 208 having net structure, and the substrate 208 is anintertexture. On any one of the first wires 2082, two adjacent secondwires 2084 are disposed on two opposite sides of the first wire 2082. Onany one of the second wires 2084, two adjacent first wires 2082 aredisposed on two opposite sides of the second wire 2084.

The first wires 2082 and the second wires 2084 can define a plurality ofcells 2086. Each cell 2086 is a through hole having quadrangle shape. Insome embodiments, the first wires 2082 are parallel with each other, thesecond wires 2084 are parallel with each other, and the cell 2086 is aparallelogram. According to the angle between the orientation directionof the first wires 2082 and the second wires 2084 and distance betweenadjacent first, second wires 2082, 2084, the cells 2086 can be square,rectangle or rhombus.

Diameters of the first wires 2082 can be in a range from about 10microns to about 5 millimeters. The first wires 2082 and the secondwires 2084 can be made of insulated materials, such as fiber, plastic,resin, and silica gel. The fiber includes plant fiber, animal fiber,wood fiber, and mineral fiber. The first wires 2082 and the second wires2084 can be cotton wires, twine, wool, or nylon wires. Particularly, theinsulated material can be flexible. Furthermore, the first wires 2082and the second wire 2084 can be made of conductive materials that arecoated with insulated materials. The conductive materials can be metal,alloy or carbon nanotube.

In one embodiment, at least one of the first wire 2082 and the secondwire 2084 is made of a composite wire comprising a carbon nanotube wirestructure and a coating layer encasing the entire carbon nanotube wirestructure. A material of the coating layer can be insulative. Theinsulative materials can be plastic, rubber or silica gel. A thicknessof the coating layer can be in a range from about 1 nanometer to about10 micrometers.

The carbon nanotube wire structure includes a plurality of carbonnanotubes joined end to end. The carbon nanotube wire structure can be asubstantially pure structure of carbon nanotubes, with few impurities.The carbon nanotube wire structure can be a freestanding structure. Thecarbon nanotubes in the carbon nanotube wire structure can besingle-walled, double-walled, or multi-walled carbon nanotubes. Adiameter of the carbon nanotube wire structure can be in a range fromabout 10 nanometers to about 1 micrometer.

The carbon nanotube wire structure includes at least one carbon nanotubewire. The carbon nanotube wire includes a plurality of carbon nanotubes.The carbon nanotube wire can be a pure wire structure of carbonnanotubes. The carbon nanotube wire structure can include a plurality ofcarbon nanotube wires parallel with each other. In other embodiments,the carbon nanotube wire structure can include a plurality of carbonnanotube wires twisted with each other.

The carbon nanotube wire can be untwisted or twisted. Referring to FIG.15, the untwisted carbon nanotube wire includes a plurality of carbonnanotubes substantially oriented along a same direction (i.e., adirection along the length direction of the untwisted carbon nanotubewire). The untwisted carbon nanotube wire can be a pure structure ofcarbon nanotubes. The untwisted carbon nanotube wire can be afreestanding structure. The carbon nanotubes are substantially parallelto the axis of the untwisted carbon nanotube wire. In one embodiment,the untwisted carbon nanotube wire includes a plurality of successivecarbon nanotube segments joined end to end by van der Waals attractiveforce therebetween. Each carbon nanotube segment includes a plurality ofcarbon nanotubes substantially parallel to each other, and combined byvan der Waals attractive force therebetween. The carbon nanotubesegments can vary in width, thickness, uniformity and shape. Length ofthe untwisted carbon nanotube wire can be arbitrarily set as desired. Adiameter of the untwisted carbon nanotube wire ranges from about 50nanometers to about 100 micrometers.

Referring to FIG. 16, the twisted carbon nanotube wire includes aplurality of carbon nanotubes helically oriented around an axialdirection of the twisted carbon nanotube wire. The twisted carbonnanotube wire can be a pure structure of carbon nanotubes. The twistedcarbon nanotube wire can be a freestanding structure. In one embodiment,the twisted carbon nanotube wire includes a plurality of successivecarbon nanotube segments joined end to end by van der Waals attractiveforce therebetween. Each carbon nanotube segment includes a plurality ofcarbon nanotubes substantially parallel to each other, and combined byvan der Waals attractive force therebetween. The length of the carbonnanotube wire can be set as desired. A diameter of the twisted carbonnanotube wire can be from about 50 nanometers to about 100 micrometers.

In one embodiment, the first wire 2082 and the second wire 2084 are bothcomposite wires, the composite wire is consisted of a single carbonnanotube wire and the coating layer.

The substrate 208 having net structure has the following advantages. Thesubstrate 208 includes a plurality of cells 2086, therefore, the soundwave generator 102 located on the substrate 208 can have a large contactarea with the surrounding medium. When the first wire 2082 or the secondwire 2084 is made of the composite wire, because the carbon nanotubewire structure can have a small diameter, the diameter of the compositewire can have a small diameter, thus, the contact area between the soundwave generator and the surrounding medium can be further increased. Thenet structure can have good flexibility, and the thermoacoustic device10 can be flexible.

Referring to FIG. 17, in a thermoacoustic device 50 according to oneembodiment, the substrate 208 can be a carbon nanotube compositestructure. The carbon nanotube composite structure includes the carbonnanotube structure and a matrix. The matrix insulates the carbonnanotube structure from the sound wave generator 102. The matrix islocated on surface of the carbon nanotube structure. In one embodiment,the matrix encases the carbon nanotube structure, the carbon nanotubestructure is embedded in the matrix. In still another embodiment, thematrix is coated on each carbon nanotubes in the carbon nanotube layer,and the carbon nanotube composite structure includes a number of poresdefined by adjacent carbon nanotubes coated by the matrix. The size ofthe pores is less than 5 micrometers. A thickness of the matrix can bein a range from about 1 nanometer to about 100 nanometers. A material ofthe matrix can be insulative, such as plastic, rubber or silica gel.Characteristics of the carbon nanotube structure are the same as thecarbon nanotube layer.

The carbon nanotube composite structure can have good flexibility. Whenthe carbon nanotube composite structure is used as the substrate 208,the thermoacoustic device 10 is flexible. If the carbon nanotubecomposite structure includes the number of pores, the sound wavegenerator 102, disposed on the carbon nanotube composite structure, canhave a large contacting surface with the surrounding medium.

Spacers

The sound wave generator 102 can be disposed on or separated from thesubstrate 208. To separate the sound wave generator 102 from thesubstrate 208, the thermoacoustic device can further include one or somespacers. The spacer is located on the substrate 208, and the sound wavegenerator 102 is located on and partially supported by the spacer. Aninterval space is defined between the sound wave generator 102 and thesubstrate 208. Thus, the sound wave generator 102 can be sufficientlyexposed to the surrounding medium and transmit heat into the surroundingmedium, therefore the efficiency of the thermoacoustic device can begreater than having the entire sound wave generator 102 contacting withthe top surface of the substrate 208.

Referring to FIGS. 20 and 21, a thermoacoustic device 70 according toone embodiment, includes a substrate 208, a number of first electrodes104 a, a number of second electrodes 104 b, a number of spacers 714 anda sound wave generator 102.

The first electrodes 104 a and the second electrodes 104 b are locatedapart from each other on the substrate 208. The spacers 714 are locatedon the substrate 208 between the first electrode 104 a and the secondelectrode 104 b. The sound wave generator 102 is located on andsupported by the spacer 714 and spaced from the substrate 208. The firstelectrodes 104 a and the second electrodes 104 b are arranged on thesubstrate 208 as a staggered manner of +−+−. All the first electrodes104 a are connected to the first conducting member 610. All the secondelectrodes 104 b are connected to the second conducting member 612. Thefirst conducting member 610 and the second conducting member 612 can beperpendicular to the first and second electrodes 104 a, 104 b.

The spacers 714 can be located on the substrate 208 between everyadjacent first electrode 104 a and second electrode 104 b and can beapart from each other for a same distance. A distance between every twoadjacent spacers 714 can be in a range from 10 microns to about 3centimeters. The spacers 714, first electrodes 104 a and the secondelectrodes 104 b support the sound wave generator 102 and space thesound wave generator 102 from the substrate 208.

The spacer 714 can be integrated with the substrate 208 or separate fromthe substrate 208. The spacer 714 can be attached to the substrate 208via a binder. The shape of the spacer 714 is not limited and can be dot,lamellar, rod, wire, and block among other shapes. When the spacer 714has a linear shape such as a rod or a wire, the spacer 714 can beparallel to the electrodes 104 a, 104 b. To increase the contacting areaof the sound wave generator 102, the spacer 714 and the sound wavegenerator 102 can be line-contacts or point-contacts. A material of thespacer 714 can be conductive materials such as metals, conductiveadhesives, and indium tin oxides among other materials. The material ofthe spacer 714 can also be insulating materials such as glass, ceramic,or resin. A height of the spacer 714 is substantially equal to orsmaller than the height of the electrodes 104 a, 104 b. The height ofthe spacer 714 is in a range from about 10 microns to about 1centimeter.

A plurality of interval spaces (not labeled) is defined between thesound wave generator 102 and the substrate 208. Thus, the sound wavegenerator 102 can be sufficiently exposed to the surrounding medium andtransmit heat into the surrounding medium. The height of the intervalspace (not labeled) is determined by the height of the spacer 714 andfirst and second electrodes 104 a, 104 b. In order to prevent the soundwave generator 102 from generating standing wave, thereby maintaininggood audio effects, the height of the interval space 2101 between thesound wave generator 102 and the substrate 208 can be in a range ofabout 10 microns to about 1 centimeter.

In one embodiment, as shown in FIGS. 20 and 21, the thermoacousticdevice 70 includes four first electrodes 104 a, and four secondelectrodes 104 b. There are two lines of spacers 714 between theadjacent first electrode 104 a and the second electrode 104 b.

In one embodiment, the spacer 714, the first electrode 104 a and thesecond electrode 104 b have a height of about 20 microns, and the heightof the interval space between the sound wave generator 102 and thesubstrate 208 is about 20 microns.

It is to be understood that, the sound wave generator 102 is flexible.When the distance between the first electrode 104 a and the secondelectrode 104 b is large, the middle region of the sound wave generator102 between the first and second electrodes 104 a, 104 b may sag andcome into contact with the substrate 208. The spacer 714 can prevent thecontact between the sound wave generator 102 and the substrate 208. Anycombination of spacers 714 and electrodes 104 a, 104 b can be used.

Thermoacoustic Device Including at Least Two Sound Wave Generators

Referring to FIG. 22, a thermoacoustic device 80 according to oneembodiment, includes a substrate 208, two sound wave generators 102, twofirst electrodes 104 a and two second electrodes 104 b.

The substrate 208 has a first surface (not labeled) and a second surface(not labeled). The first surface and the second surface can be oppositewith each other or adjacent with each other. In one embodiment accordingto FIG. 22, the first surface and the second surface are opposite witheach other. The substrate 208 further includes a plurality of recesses208 a. In the embodiment according to FIG. 22, each recess 208 a is athrough hole located between the first surface and the second surface.The plurality of recesses 208 a can be parallel with each other.

One sound wave generator 102 is located on the first surface of thesubstrate 208 and electrically connected with one first electrodes 104 aand one second electrodes 104 b. The other one sound wave generator 102is located on the second surface of the substrate 208 and electricallyconnected with the other one first electrode 104 a and the other onesecond electrode 104 b.

Referring to FIG. 23, a thermoacoustic device 90 including a pluralityof sound wave generators 102 is provided. The thermoacoustic device 90includes a substrate 208. The substrate 208 includes a plurality ofsurfaces, one sound wave generator 102 is located on one surface. Thethermoacoustic device 90 can further include a plurality of firstelectrodes 104 a and a plurality of second electrodes 104 b. Each soundwave generator 102 is electrically connected with one first electrode104 a and one second electrode 104 b. In the embodiment according toFIG. 23, the thermoacoustic device 90 includes four sound wavegenerators 102, and the substrate 208 includes four surfaces. The foursound wave generators 102 are located on the four surfaces in a one byone manner. The surfaces can be planar, curved or include someprotuberances.

The thermoacoustic device including two or more sound wave generators102 can emit sound waves to two or more different directions, and thesound generated from the thermoacoustic device can spread. Furthermore,if there is something wrong with one of the sound wave generators, theother sound wave generator can still work.

Thermoacoustic Device Using Photoacoustic Effect

In one embodiment, the signal input device 104 can be a light sourcegenerating light signals. The light signals can be directly transferredto the sound wave generator 102, and the thermoacoustic device worksunder a photoacoustic effect. The first and second electrodes 104 a, 104b are nod needed. The photoacoustic effect is a kind of thethermoacoustic effect and a conversion between light and acousticsignals due to absorption and localized thermal excitation. When rapidpulses of light are incident on a sample of matter, the light can beabsorbed and the resulting energy will then be radiated as heat. Thisheat causes detectable sound signals due to pressure variation in thesurrounding (i.e., environmental) medium.

Referring to FIG. 24, a thermoacoustic device 100 according to oneembodiment includes a signal input device 104, a sound wave generator102 and a substrate 208, but it does not have the first and secondelectrodes. In the embodiment shown in FIG. 24, the substrate 208 has atop surface (not labeled) and includes at least one recess 208 a. Thesound wave generator 102 is located on the top surface of the substrate208.

The signal input device 104 is located apart form the sound wavegenerator. The signal input device 104 can be a laser-producing device,a light source, or an electromagnetic signal generator. The signal inputdevice 104 can transmit electromagnetic wave signals 1020 (e.g., lasersignals and normal light signals) to the sound wave generator 102. Insome embodiments, the signal input device 104 is a pulse laser generator(e.g., an infrared laser diode). A distance between the signal inputdevice 104 and the sound wave generator 102 is not limited as long asthe electromagnetic wave signal 1020 is successfully transmitted to thesound wave generator 102.

In the embodiment shown in FIG. 24, the signal input device 104 is alaser-producing device. The laser-producing device is located apart fromthe sound wave generator 102 and faces to the sound wave generator 102.The laser-producing device can emit a laser. The laser-producing devicefaces to the sound wave generator 102. In other embodiments, when thesubstrate 208 is made of transparent materials, the laser-producingdevice can be disposed on either side of the substrate 208. The lasersignals produced by the laser-producing device can transmit through thesubstrate 208 to the sound wave generator 102.

The sound wave generator 102 absorbs the electromagnetic wave signals1020 and converts the electromagnetic energy into heat energy. The heatcapacity per unit area of the carbon nanotube layer is extremely small,and thus, the temperature of the carbon nanotube layer can changerapidly with the input electromagnetic wave signals 1020 at thesubstantially same frequency as the electromagnetic wave signals 1020.Thermal waves, which are propagated into surrounding medium, areproduced. Therefore, the surrounding medium, such as ambient air, can beheated at an equal frequency as the input of electromagnetic wave signal1020 to the sound wage generator 102. The thermal waves produce pressurewaves in the surrounding medium, resulting in sound wave generation. Inthis process, it is the thermal expansion and contraction of the mediumin the vicinity of the sound wave generator 102 that produces sound. Theoperating principle of the sound wave generator 102 is the“optical-thermal-sound” conversion.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the invention. Variations may be made tothe embodiments without departing from the spirit of the presentdisclosure as claimed. Any elements discussed with any embodiment areenvisioned to be able to be used with the other embodiments. Theabove-described embodiments illustrate the scope of the invention but donot restrict the scope of the present disclosure.

What is claimed is:
 1. A thermoacoustic device comprising: a sound wavegenerator comprising a graphene layer, wherein the graphene layercomprises at least one graphene, and the graphene layer is configured toconvert electromagnetic wave signals into heat energy to heatsurrounding medium to produce sound waves; and a signal input deviceconfigured to input the electromagnetic wave signals to the sound wavegenerator.
 2. The thermoacoustic device of claim 1, wherein the graphenelayer comprises a plurality of graphenes stacked with each other orlocated side by side.
 3. The thermoacoustic device of claim 1, whereinthe graphene layer is a pure structure of graphenes.
 4. Thethermoacoustic device of claim 1, wherein a thickness of the graphenelayer is less than 200 nanometers.
 5. The thermoacoustic device of claim1, wherein a heat capacity per unit area of the graphene layer is lessthan or equal to 2×10⁻³ J/cm²*K.
 6. The thermoacoustic device of claim1, wherein the signal input device comprises at least one firstelectrode and at least one second electrode, and the sound wavegenerator is electrically connected with the at least one firstelectrode and the at least one second electrode.
 7. The thermoacousticdevice of claim 6, wherein the signal input device comprises a pluralityof first electrodes and a plurality of second electrodes, and theplurality of first electrodes and the plurality of second electrodes aresubstantially parallel to each other and arranged in a staggered manner.8. The thermoacoustic device of claim 6, wherein each of the at leastone first electrode and the at least one second electrode is a linearcarbon nanotube structure comprising a plurality of carbon nanotubesjoined end to end with each other.
 9. The thermoacoustic device of claim8, wherein the plurality of carbon nanotubes are parallel with eachother and oriented along an axial direction of the linear carbonnanotube structure.
 10. The thermoacoustic device of claim 1, furthercomprising a substrate, wherein the sound wave generator is located on asurface of the substrate.
 11. The thermoacoustic device of claim 10,wherein the signal input device comprises a plurality of firstelectrodes and a plurality of second electrodes, the plurality of firstelectrodes and the plurality of second electrodes are located betweenthe substrate and the sound wave generator, and at least part of thesound wave generator is suspended above the substrate by the pluralityof first electrodes and the plurality of second electrodes.
 12. Thethermoacoustic device of claim 10, wherein the substrate defines atleast one recess through the surface, and the sound wave generatorcovers the at least one recess and is suspended above the at least onerecess.
 13. The thermoacoustic device of claim 12, wherein the at leastone recess is a blind hole, through hole, blind groove or throughgroove.
 14. The thermoacoustic device of claim 12, wherein the substratedefines a plurality of recesses through the surface located uniformly.15. The thermoacoustic device of claim 10, further comprising aplurality of spacers located between the sound wave generator and thesubstrate, and the sound wave generator is elevated above the substratevia the plurality of spacers.
 16. The thermoacoustic device of claim 15,wherein the signal input device comprises at least one first electrodeand at least one second electrode located between the sound wavegenerator and the substrate, the at least one first electrode and atleast one second electrode contact the surface of the substrate and thesound wave generator, and the plurality of spaces is located on thesurface of the substrate and between the at least one first electrodeand the at least one second electrode.
 17. The thermoacoustic device ofclaim 10, wherein the substrate has a net structure comprising aplurality of first wires and a plurality of second wires, the pluralityof first wires is oriented along a first direction and disposed apartfrom each other, the plurality of second wires is oriented along asecond direction and disposed apart from each other, and an angle thatis defined between the first direction and the second direction is in arange from about 0 degrees to about 90 degrees.
 18. The thermoacousticdevice of claim 1, wherein the signal input device is a laser-producingdevice, a light source, or an electromagnetic signal generator.
 19. Athermoacoustic device comprising: a sound wave generator consisting of agraphene layer, wherein the graphene layer is a pure structure ofgraphenes, and the graphene layer is configured to convertelectromagnetic wave signals into heat energy to heat surrounding mediumto produce sound waves; and a signal input device configured to inputthe electromagnetic wave signals to the sound wave generator.
 20. Thethermoacoustic device of claim 1, wherein the signal input devicecomprises at least one first electrode and at least one secondelectrode, and the sound wave generator is located on the at least onefirst electrode and the at least one second electrode.